1. Field of the Invention
The present invention relates to an ink-jet recording head in which a pressure generating chamber ejects ink in the form of ink droplets or drops by utilization of elastic deformations of an elastic plate as a part of the pressure generating chamber, which are caused by a piezoelectric transducing element. More particularly, the invention relates to the structure of a passage forming substrate.
2. Description of the Related Art
The ink-jet recording head (referred often to as a printhead) includes an ink passage unit. The ink passage unit is composed of a reservoir for receiving ink from an ink tank externally provided, pressure generating chambers formed as cavities to which pressure is applied, ink supply ports each communicatively connecting a reservoir with a pressure generating chamber, a passage forming substrate having nozzle passage holes formed as through-holes each communicated with a pressure generating chamber and a discharge orifice, an elastic plate being sealingly applied to one of the major surfaces of the passage forming substrate, a nozzle plate with discharge orifices being sealingly applied to the other major surface of the passage forming substrate, and piezoelectric transducing elements are provided on the elastic plate. A pressure generating chamber is expanded and contracted by utilization of displacement of a piezoelectric transducing element associated with the pressure generating chamber. When the pressure generating chamber is expanded, the pressure generating chamber sucks ink from a reservoir associated therewith, through an ink supply port also associated therewith. When contracted, the pressure generating chamber pressurizes ink contained therein to forcibly discharge the ink in the form of an ink drop, through the discharge orifice associated therewith.
When color inks are used, the ink-jet printhead is capable of performing a full color printing. Because of this feature, the printhead is used for a color printer and its use has rapidly become widespread. In this respect, there is a consistent demand of further improvement of the quality of the print by the ink-jet printhead.
The print quality of this type of printhead depends largely on the size of dots formed by the ink drops ejected from the printhead and a print density of the print by the printhead. To increase the print density, it is essential to reduce the volume of one ink drop as small as possible, viz., the size of the dot formed by it.
To this end, the necessity is to array pressure generating chambers at the highest density and to substantially prevent or minimize a deformation of the passage forming substrate. Further, for ease of handling in assembling the printhead, it is necessary to reduce the volume of each pressure generating chamber and to array the chambers at high density. In connection with this, Japanese Patent Laid-Open Publication No. Sho-58-40509 discloses such a novel technique in that a silicon monocrystalline substrate having a face is lithographically and anisotropically processed to form therein recesses being shallow in depth and small in their opening area, and the recesses are used as pressure generating chambers or cavities while being densely arrayed.
Each pressure generating chamber thus formed is flat. The flat pressure generating chamber is large in its flow resistance. A smoothness of the supplying of ink from the reservoir to the pressure generating chamber is lost. A possible measure to address this problem is to enlarge the ink supplying passages without increasing the volume on the ink drop, specifically to additionally provide second pressure generating chambers in the part of the silicon monocrystalline substrate, located on the opposite side from the side where the piezoelectric transducing elements are formed, viz., the part where the discharge orifices are formed. This measure suffers from another problem, however. That is, a velocity of flow of the ink flowing from the reservoir to the pressure generating chamber is decreased. Where the flow velocity of ink is low, bubbles tend to remain in the pressure generating chambers located closer to the piezoelectric transducing elements. The result is to deteriorate a quality of the resultant print.